General

The ContextPathBuilder does not support this
for a good reason. A context is a dynamic entity which is bound to an
arbitrary server. So you can't guarantee were your context is running
in a distributed environment. If you still need the full URL, extend the
ContextPathBuilder and override the getUserFilesPath
method and return the full URL.

Localization

Unfortunately the JavaScript code which responds with error messages
is incomplete. It does not cover all error numbers and has static error
messages. You can fix this by searching for all files which read the GetResponse
or UploadResponse and let the switch clause simply alert your localized
message.